A multiconfigurational hybrid density-functional theory.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Standard hybrid density-functional approximations (DFAs) include exact exchange but neglect static correlation.
• Many chemical processes, such as bond dissociation and cycloaddition reactions, involve significant static correlation.
• Existing DFT methods struggle to accurately describe systems with strong static correlation.

Purpose of the Study:

• To develop a novel multiconfigurational hybrid density-functional theory (DFT) method.
• To rigorously combine multiconfiguration self-consistent-field (MCSCF) calculations with DFAs.
• To improve the description of chemical systems with strong static correlation effects.

Main Methods:

• The proposed method combines MCSCF calculations with a DFA based on linear decomposition of electron-electron interaction.
• It extends hybrid approximations by adding a fraction (λ) of exact static correlation alongside exact exchange.
• Test calculations were performed using Perdew-Burke-Ernzerhof (PBE) and Becke-Lee-Yang-Parr (B3LYP) functionals.

Main Results:

• A value of λ = 0.25 was found to be optimal, consistent with standard hybrid approximations.
• The method was tested on cycloaddition reactions of ozone with ethylene/acetylene and diatomic molecule dissociation.
• Results indicate improved accuracy compared to standard DFT for systems with strong static correlation.

Conclusions:

• The proposed multiconfigurational hybrid approximations offer a promising advancement in DFT.
• This method provides a more accurate treatment of static correlation effects in quantum chemical calculations.
• It shows potential for broader application in studying challenging chemical phenomena.